1. Field of the Invention
The present invention relates to cured siloxane dielectric films and to a process for their production by electron beam exposure. Such films are useful in the manufacture of integrated circuits (IC's).
2. Description of the Related Art
A continuing trend in the field of semiconductor technology is the formation of integrated circuit chips having more and faster circuits thereon. Such ultralarge scale integration has resulted in a continued shrinkage of feature sizes with the result that a large number of devices are available on a single chip. With a limited chip surface area, the interconnect density typically expands above the chip substrate in a multi-level arrangement and so the devices have to be interconnected across these multiple levels.
The interconnects must be electrically insulated from each other except where designed to make contact. Usually electrical insulation requires depositing dielectric films onto a surface. It is known in the art that siloxane resins are usefull in the electronic and semiconductor fields to provide a dielectric coating to silicon wafers and other components. Such coatings protect the surface of substrates and form dielectric layers between electric conductors on IC's. Such coatings can be used as protective layers, interlevel dielectric layers, doped dielectric layers to produce transistor like devices, capacitor and capacitor like devices, multilayer devices, 3-D devices, silicon on insulator devices, coatings for superconductors, and the like.
As mentioned above, semiconductor devices often have multiple arrays of patterned interconnect levels that serve to electrically couple individual circuit elements thus forming an integrated circuit. In the past, these interconnect levels have been separated by such insulating dielectric films as a silicon oxide film formed using chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD) techniques. However, as the size of circuit elements and the spaces between such elements decreases, the relatively high dielectric constant of such silicon oxide films has become a problem.
In order to provide a lower dielectric constant than that of silicon oxide, dielectric films formed from siloxane based resins are becoming widely used. The production of siloxane resins is well known in the art. In this regard, see U.S. Pat. Nos. 3,615,272; 4,756,977; 5,010,159 and 4,999,397. However, while such siloxane films do provide lower dielectric constants than CVD or PECVD silicon oxide films it has been found that typically the dielectric constants of such films are limited to approximately 3.0 or greater. The dielectric constant of such insulating films is an important factor where IC's with low power consumption, crosstalk, and signal delay are required. As IC dimensions continue to shrink, this factor increases in importance. As a result, siloxane based resin materials that can provide insulating films with dielectric constants below 3.0 are very desirable. In addition, it would be desirable to have a siloxane based resin which have a high resistance to cracking and low stress when formed in thicknesses of approximately 1.0 .mu.m or greater. It has now been found that such crack resistant, low stress films can be produced when the particular organic siloxane resins of the present invention are cured using electron beam exposure.
Another problem with siloxane based resins is that they must be cured to be effective as a dielectric. Specifically, after a semiconductor wafer having metal lines is coated with the siloxane and cured, it must be resistant to oxygen plasmas in subsequent IC production operations. In the prior art, siloxane polymers have been thermally cured. Unfortunately, thermal curing leaves SiOH bonds in the siloxane polymer. When thermally cured siloxanes are then subjected to oxygen plasma, water is produced by the hydration of the SiOH bonds thus poisoning vias cut through the dielectric in a non-etchback process. It has now been unexpectedly found that electron beam curing changes the properties of the siloxane such that essentially no hydrogen remains after exposure. Thus water formation is avoided or significantly reduced. This results in a denser SiO-SiO structure, minimizing formation of a hydrated film and poisoned vias. In addition, electron beam exposure is much faster than thermal curing, thus increasing IC throughput.